Read Glasslands, then Thursday War and then if you have time, I do recommend reading Cryptum and Primordium. The Forerunner books give more insight into the Didact, and since he is the antagonist in Halo 4 it might help to have some background information on him.

Yeah, I've read cryptum like a week ago from the library. Prim. Glasslands and the thursday war I ordered on amazon. Primoriduim isn't on Amazon until the 30th so 5 to 8 business days will be past H4, and even if it does come before I can't read a book in one day.